1. Field of the Invention
The present invention relates to a wiring board.
2. Description of the Related Art
Conventionally, a technique to increase the density of wirings, in other words, a technique to form high-density wiring layers, in a wiring board in which a passive component is included, has been studied. Specifically, a wiring board is known in which a layer including a stacked structure of photosensitive resin, in which the density of wirings is higher (hereinafter, referred to as a “high-density wiring layer”), is formed on a layer composed of a stacked structure of thermosetting resin, in which the density of wirings are lower (hereinafter referred to as a “low-density wiring layer”). Here, the passive component is included in the low-density wiring layer.
For example, Patent Document 1 discloses that in such a wiring board, by adopting a method of embedding a wiring layer formed at a surface of a core substrate, which is the low-density wiring layer, in an insulating layer (thermosetting resin) formed at the surface of the core substrate and forming a high-density wiring layer thereon, the density of wirings of the high-density wiring layer can be made higher.
However, according to the above described method, it is still difficult to form fine wirings on the insulating layer (thermosetting resin) formed at the surface of the core substrate, and it is necessary to form an insulating layer made of photosensitive resin on the insulating layer (thermosetting resin). Then, the fine wirings are formed thereon.
This means that, as it is still difficult to form the fine wirings directly on the insulating layer (thermosetting resin) formed at the surface of the core substrate just by embedding the wiring layer formed at the surface of the core substrate in the insulating layer (thermosetting resin), there remains a problem in actualizing a high-density wiring layer.